The present invention relates to microbial enhanced oil recovery (MEOR) based on the use of denitrifying microorganisms.
Petroleum is recovered from underground oil-bearing rock formations by penetrating a rock formation with one or more wells and collecting the oil at the surface. If sufficient pressure exists in the underground oil-bearing rock formations, the oil is forced to the surface by the pressure without the need for a pump. Frequently, as a reservoir becomes depleted, the pressure in the reservoir decreases to the point where pumping is required.
Unfortunately, much of the oil in underground rock formations is contained in pockets which are isolated from the space being accessed by a well bore. Oil contained in isolated pockets is difficult to recover by conventional methods, such as drilling additional well bores to access these pockets.
At the present time, the average recovery of oil from an underground reservoir ranges from 10% to 50% with an average of about 33%. Since an estimated 67% of the United States' oil reserves are still in the ground and not recoverable using current technology, the ability to efficiently recover even 1% of the oil trapped in pockets would result in significant economic benefits and would decrease the United States' dependence on foreign oil. There is still an estimated 35.times.10.sup.10 barrels of oil left in "exhausted" United States oil fields, not including oil shale. Approximately 15-40% of the oil contained in "exhausted" oil fields is in rock formations containing significant amounts of carbonate.
Accordingly, there is a need for a practical method of recovering oil from underground rock formations which contain oil in isolated pockets.